<script>
    var count1 = 0;
    var count2 = 200;
    var count3 = 100;

    console.log(count1 && count2);  // false
    console.log(count2 && count3);  // true

    // 逻辑与的妙用
    var obj = null;
    // console.log(obj.a); 
    obj && obj.a;

</script>